Add version rollback support for AppImage updates

src/ui/update_dialog.rs

@@ -184,6 +184,14 @@ fn start_update(
                 dialog.set_body(&success_body);
                 dialog.set_response_enabled("update", false);
 
+                // Save previous version path for rollback
+                if let Some(ref old_path) = applied.old_path_backup {
+                    db_ref.set_previous_version(
+                        record_id,
+                        Some(&old_path.to_string_lossy()),
+                    ).ok();
+                }
+
                 // Handle old version cleanup
                 if let Some(old_path) = applied.old_path_backup {
                     handle_old_version_cleanup(&dialog, old_path);